Capnography is often defined as the measurement of the level of carbon dioxide (CO2) in exhaled and/or inhaled breath. Since infrared light was found to be absorbed particularly well by CO2, capnographs usually measure infrared absorption in the breath gasses, which indicates the level of CO2 in these gasses. Other measurement technologies exist as well.
The information obtained from a capnographic measurement is sometimes presented as a series of waveforms, representing the partial pressure of CO2 in the patient's exhaled breath as a function of time.
Clinicians commonly use capnography in order to assess a patient's ventilatory status. Respiratory arrest and shunt may be speedily diagnosed, and a whole range of other respiratory problems and conditions may be determined by the capnographic measurement. Capnography is considered to be a prerequisite for safe intubation and general anesthesia, as well as for correct ventilation management.
Breath flow dynamics is another ventilation-related factor that is sometimes being measured. Whereas capnography is usually indicative of physiological aspects of ventilation, breath flow dynamics measurement is often indicative of the mechanics of respiration—the inhalation and exhalation activity of patient's lungs.